The pressures mentioned here are absolute pressures.
Industrial synthetic hydrocarbon production units called GTL (Gas-To-Liquid) units may have a production capacity of around 50 000 barrels per day, which corresponds to a consumption of about 12 000 metric tons of oxygen per day.
To produce such quantities of oxygen, it is necessary to provide several, typically three or four, air distillation units in parallel. In addition, to bring the oxygen to the high pressure needed for operating the GTL unit, it is advantageous for the liquid oxygen produced by distillation to be pumped to this high pressure and for the liquid to be vaporized by heat exchange with a heat transfer fluid compressed to a pressure high enough to allow oxygen to vaporize, this heat transfer fluid typically being pressurized air. Thus, the use of gaseous oxygen compressors, which is always tricky, is avoided.
Such plants are described in “Oxygen Facilities for Synthetic Fuel Projects” by W. J. Scharle et al., Journal of Engineering for Industry, November 1981, Vol. 103, pp. 409–411.